一质点沿x轴做加速运动,它离开O点的距离随时间t的变化关系为x=5+2t3,其中

题型:选择题

问题:

一质点沿x轴做加速运动,它离开O点的距离随时间t的变化关系为x=5+2t3,其中x的单位是m,t的单位是s,它的速度v随时间t的变化关系是v=6t2,其中t的单位是s。设该质点在t=0到t=2s间的平均速度为v1t=2s到t=3s间的平均速度为v2,则(   )

A.v1=12m/s

B.v1=8m/s

C.v2=38m/s

D.v2=39m/s

考点:匀变速直线运动
题型:选择题

IMPROVE ON SLEEP

Good health needs a good sleep. Going to bed before you’re tired. Not eating or reading in bed. Go to bed at the same time before midnight and get up at the same time. Your body likes routine (常规) for a good night’s sleep.

STAY FREE OF FLU

Studies show that a cold or flu virus (病毒) can live on our hands for long. So wash all parts of your hands often with soap and water. For more ways to prevent (阻止)the spread of flu, please call HealthLine at 1800 848 1313.

ORAL (口腔) HEALTH

Brush your teeth twice daily and visit the dentist at least once a year. The mouth is a mirror (镜子)of disease(疾病). The oral examination (检查)is not only for the health of teeth, but the whole body. For more of it, please visit www. mydr. com. au.

FIT FOR LIFE

Studies have shown that many diseases have something to do with less or no physical (身体) activity. Try to do it for 30 minutes a day, 5 days or more a week. For more information, please call HealthLine at 1800 438 2000.

小题1:If you want to get a good sleep, you’d better _______.

A.go to bed after you’re tired

B.go to sleep at midnight

C.follow the bedtime routine

D.eat something or read in bed小题2:To prevent from catching a cold or flu, it’s good for you _______.

A.to clean your fingers often

B.to brush your teeth twice daily

C.to get up early every morning

D.to wash all parts of your hands小题3:You should visit the dentist at least once a year, because _______.

A.the oral examination is necessary

B.you don’t often brush your teeth

C.some diseases may be in the mirror

D.you don’t have a good night’s sleep小题4:Studies have shown that many diseases have something to do with _______.

A.having no oral examination

B.washing hands with cold water

C.sleeping too late sometimes

D.doing little physical activity小题5:When you want to learn more about the flu, you can _______.

A.visit www. mydr. com. Au

B.call HealthLine at 1800 848 1313

C.visit the dentist in your place

D.call HealthLine at 1800 438 2000

题型:选择题

对称负载采用星形连接或三角形连接,在电源线电压相等的条件下,它们的有功功率不相等。()

题型:选择题

()只能在封闭的机构中使用。

A、滴油润滑

B、油环润滑

C、飞溅润滑

D、压力循环润滑

题型:选择题

机动车驾驶人只要喝酒没醉仍可驾车。

题型:选择题

丁烯-1产品组成中MTBE的设计含量是()。

A、≤10mg/kg

B、≤25mg/kg

C、≥10mg/kg

D、≥25mg/kg

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